Natural oakmoss extracts are of fundamental importance to the perfume industry. They are used, for example, as important components of perfumes, "Chypre" and "Fougere" being noted.
Natural oakmoss is only available in limited quantities. Therefore, it is necessary to use synthetic substitutes with an oakmoss character. It is especially advantageous if the synthetic substances are naturally identical, i.e. components of natural oakmoss extract, and simultaneously exhibit the characteristic oakmoss aroma. For example, 3,6-dimethyl-.beta.-resorcylic acid methyl ester is such an ingredient. It was first isolated from oakmoss oil by H. Waldbaum and A. Rosenthal/Ber. Duet. Chem Ges. 57B, 770 (1924)/.
A number of methods are known for preparing alkyl-substituted .beta.-resorcylic acid esters from alkylated dihydro .beta.-resorcylic acid esters. Dihydroresorcylic acid esters are readily obtained by condensation of .alpha., .beta.-unsaturated carboxylic acid esters with .beta.-keto esters [cf. A. Sonn, Ber. Deut. Chem. Ges. 62B, 3012 (1929)] or by condensation of malonic acid esters with .alpha., .beta.-unsaturated ketones [cf. U. Steiner and B. Wilhelm, Helv. Chim. Acta 35, 1752 (1952)].
A. Sonn [Ber. Duet. Chem. Ges. 62B, 3012 (1929)] dehydrated dihydroresorcylates using expensive palladium catalyst. German Auslegeschrift No. 19 41041 and U.S. Pat. No. 3,634,491 of IFF Inc., New-York, describes oxidation with chlorine or chlorine-generating substances. Oxidation can also be performed with bromine in glacial acetic acid (U.S. Pat. No. 3,884,843, Fritzsche Dodge & Olcott Inc., N.Y.). The result is the dibromo-substituted aromate, which is dehalogenated with the aid of Raney nickel. However, the use of halogens or halogen-generating substances for oxidation requires special safety measures and special reactors, since these substances can have a toxic and poluting effect.
M. S. Kablaoui [J. Org. Chem. 39, 3696 (1974)] aromatized various substituted and unsubstituted cyclohexane-diones, heating them with a mixture of acetic anhydride and sulphuric acid. The reaction mechanism postulated by Kablaoui, however, would necessarily require a dione structure, so that transfer to structurally different classes of compounds does not appear possible.